1. Field of Invention
The present invention relates generally to a MEMS (micro-electronic mechanical system) sensor unit for wireless security applications that provides an extended battery life for the MEMS sensor unit, to provide both immediate MEMS motion detection, and also an “out of range” detection capability when the MEMS sensor unit is moved beyond the range of a security system receiver, providing both capabilities without an unacceptable reduction in battery life for the MEMS sensor unit.
2. Discussion of the Prior Art
Prior art wireless security systems have protected valuable assets by attaching to each asset a battery powered security tag that periodically transmits a short range security RF signal to a security system receiver that monitors the signals within a protected safe area defined by the range within which the security system receiver can normally receive and detect the short range signals transmitted by the security tag. The range that a security system receiver can normally receive and detect transmitted short range RF signals is typically 200 to 300 feet within a building and can extend up to one mile over open space. A typical prior art security system can include several different receivers strategically placed around a security area being protected The security system assumes that the asset is safe as long as the security system receiver continues receiving the periodically transmitted security signals, and assumes an alarm condition when the security system receiver stops receiving the periodically transmitted security signals.
MEMS sensors are generally used in the prior art to measure and indicate motion immediately as the sensors are moved in one or more directions. In a wireless security system, a battery powered unit including a MEMS sensor and a transmitter can be attached to a valuable object to be protected, and when the MEMS sensor detects that the object is being moved, the unit transmits a wireless short range RF signal to a security system receiver. For broader applications in the security industry, an ideal MEMS sensor unit would provide immediate MEMS motion detection, and also provide an “out of range” detection capability when the MEMS sensor unit is moved beyond the range of the security system receiver. In this second “out of range” application, a logical way to provide a notification to the security system is for the MEMS sensor unit to transmit signals on a frequent periodic basis, such as on a periodic basis of once every minute. In such an arrangement, the battery life of the transmitter would be severely diminished, and the reduced battery life would not be acceptable in many different security situations. The present invention provides a solution whereby both applications can be met without an unacceptable reduction in battery life for the MEMS sensor unit.